; ; ; ; ; ; ;


FLOOD Ed.
What you should know about floods and then some.
Search Flood Ed:


FLOOD NEWS

Levee protection methods debated at meeting
Jul 23, 2013




Ongoing tension continued Thursday between the board overseeing the East Bank’s flood protection system and the U.S. Army Corps of Engineers over how to ensure the area’s levees hold if they get overtopped during storm surges.

The Southeast Louisiana Flood Protection Authority-East is calling on the corps to slow down as it considers how to “armor” levees and to consider concerns about the extent of its plans and the way it plans to prevent the barriers from failing during a storm.

Armoring involves protecting the levees from being scoured away during a storm. The options now being considered by the corps for the New Orleans-area levees are focusing on the use of grass that in some cases would be reinforced with mats.

The corps plans to make recommendations in the next several months on the types of armoring that should be used. The levee authority has submitted questions and comments on that plan, but board members expressed concerns that the pace the process is moving at could preclude their input.

“We want you all to slow down and consider all the points we’ve made,” board President Tim Doody said.

However, he also acknowledged the corps is under pressure to finish the system.

In his first presentation to the board responsible for the East Bank flood protection system, Col. Richard Hansen, the corps commander for the New Orleans district, and his staff were grilled on the corps’ plans. “Your comments are being looked at very hard,” Hansen told the board.

Armoring remains one of the last outstanding issues in the construction of the post-Hurricane Katrina levee system. While massive levees are among the most visible elements of the defensive perimeter, the kind of grass that covers them is considered to be one of the most important elements of ensuring the system works.

That covering is vital in cases where the levees are overtopped, sending water rushing down their protected side, which is their interior slope. That wouldn’t necessarily lead to a disaster but in that situation, unprotected or poorly protected property can be eroded away, weakening the levee and leading to a breach and the failure of the protective system.

The dire consequences of such a situation were laid out in the report that analyzed why the federal levee system failed after Katrina. The report found the majority of 50 levee and floodwall breaches during the storm occurred after those structures had been overtopped by storm surge and were then eroded by the floodwaters.

All of the levees that breached during the storm were overtopped, according to the report.

Several options are being considered for the system, including regular grass, “enhanced” grass specially grown to prevent erosion and even reinforced turf mats.

Reinforced mats provide the greatest degree of protection, though corps officials have said modeling they’ve done, along with tests at a specially designed facility at Colorado State University, have shown it is not necessary in all areas.

The evaluation included testing grass and mats that had been “distressed,” simulating the effects of a drought, and those effects are being taken into account in the corps’ recommendations.

The corps’ plans call for about 8 miles of the East Bank levees to be covered with the mat-reinforced grass and another 10 miles to be covered with grass. That would leave essentially the entire lakefront with only regular grass protecting against erosion.

While the post-Katrina report focused on the importance of armoring the levees to prevent breaches, the flood protection authority’s regional director, Bob Turner, said regular grass wasn’t “what they had in mind.”

The corps’ armoring plans focuses on the protected side of the levees, but Commissioner Paul Kemp also questioned whether additional protection should be added on the unprotected side, which faces the water. Some levees experienced erosion on their unprotected side during Katrina, Kemp said.

Commissioner John Barry said it was crucial to get the proper armoring in place. “This system will be overtopped,” Barry said. “It’s inevitable.”